NCERT Solutions for Class 9th Social Science Chapter 3 The chapter's recap points, expanded — Before we move on …

Book page 56–57 Updated on2026-09-08

Q1.

The Earth's atmosphere is made up of different gases, mainly nitrogen and oxygen, along with small amounts of other gases like water vapour and dust, support life and help in forming clouds and causing rainfall.

Answer

What this recap means, expanded. The recap packs three separate ideas into one line — what the air is made of, that it supports life, and that it makes weather. Take them one at a time.

Component	Share (Fig. 3.2)	What it does
Nitrogen	78%	The largest share by far. Plants cannot take it from the air directly — nitrogen-fixing bacteria convert it into a form roots can absorb, and from there it becomes protein in every living body
Oxygen	21%	What we breathe; essential to life on the Earth
Argon	0.93%	The largest of the trace gases, and chemically inactive
Carbon dioxide	0.04%	Used by plants; also the greenhouse gas at the centre of climate change later in the chapter
Other gases	0.03%	Helium, neon, krypton, xenon, ozone, hydrogen — tiny quantities, but ozone in the stratosphere is what filters ultraviolet radiation
Water vapour	0.1 – 0.4%	Varies constantly. It plays a significant role in cloud formation and precipitation — no water vapour, no rain
Dust particles	tiny	Water vapour needs a surface to condense on. Dust supplies it, which is why dust matters to cloud formation out of all proportion to its amount

Check the pie adds up:
78 + 21 + 0.93 + 0.04 + 0.03 = 100.00%
Nitrogen and oxygen alone = 78 + 21 = 99%
So everything else together = 100 − 99 = 1%

Why the same air both supports life and makes weather: because the two jobs are done by different parts of the mixture. Life depends on the steady 99% — nitrogen and oxygen, in proportions that barely change. Weather depends on the part that does change: water vapour swinging between 0.1% and 0.4%, and the dust it condenses on. A constant gas cannot produce a variable sky; a variable one can.

Q2.

The atmosphere is made up of different layers, namely the Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere, which are divided based on changes in temperature and air density as we go higher above the Earth's surface.

Answer

What this recap means, expanded. The five layers are not five different substances — the air is much the same mixture throughout the lower layers. What changes is temperature and density, and it is those two changes that draw the boundaries.

Layer	Extends to	Thickness	Temperature with altitude	Its landmark feature
Troposphere	about 12 km	12 km	Falls	Nearly all weather; most water vapour and clouds; the air we breathe
Stratosphere	50 km	38 km	Rises	The ozone layer; aeroplanes fly here
Mesosphere	80 km	30 km	Falls	Meteorites burn up
Thermosphere	700 km	620 km	Rises very rapidly	Ionosphere reflects radio waves; auroras
Exosphere	fades into space	—	—	Very thin air; helium and hydrogen escape

Work out the thicknesses from the chapter's own heights:
Troposphere = 12 − 0 = 12 km
Stratosphere = 50 − 12 = 38 km
Mesosphere = 80 − 50 = 30 km
Thermosphere = 700 − 80 = 620 km
So the troposphere is only 12 km of the roughly 700 km measured here — about 1.7% of the height — and yet nearly all the weather happens inside it.

The three boundaries have names of their own, and each marks the point where the temperature stops going one way and turns the other: the tropopause (troposphere / stratosphere), the stratopause (stratosphere / mesosphere) and the mesopause (mesosphere / thermosphere).

Why density is the second criterion, and why it behaves more simply than temperature: density just falls, all the way up, without reversing — the chapter says it is highest near the Earth's surface and decreases with altitude. That is gravity: the air near the ground is squeezed by the weight of all the air above it, and there is less and less weight above you as you rise. Temperature, by contrast, reverses four times, because it depends on where the heating comes from in each layer. Two different rules, two different patterns — and together they cut the atmosphere into five.

Q3.

Weather refers to the daily atmospheric conditions, while climate is the average weather of a place over a long period of time.

Answer

What this recap means, expanded. Same atmosphere, same five elements — the difference is entirely one of time and area.

	Weather	Climate
Definition in the chapter	The hour-to-hour and day-to-day conditions of the atmosphere	The sum total of weather conditions and variations over a large area for an extended period, usually thirty years or more
Area	A single place	A large region
How it changes	Can vary significantly from day to day	Changes only over decades
Example from this chapter	'Is it going to rain today?' — and the two-week newspaper record in LET'S ANALYSE	'The climate of India can be broadly classified as tropical monsoon' — and the averages in Table 3.3

Both are built from the same five elements, which the chapter lists as the major ones that impact human life: temperature, precipitation, humidity, wind and atmospheric pressure. Read those five for today and you have described the weather; average them over thirty years and you have described the climate.

Why thirty years, and not three or three hundred: a short record is dominated by chance — one freak year would tilt the whole average. Thirty years is long enough for the good monsoons and the failed ones to balance out, so that what is left is the genuine character of the place. That is why every number in Table 3.3 is called an average monthly figure: no single January in Delhi was exactly 14.4°C, but the typical one is.

Where this matters most: climate change is defined in this chapter as a long-term change in weather patterns. It can only be detected by comparing one long average with another — never by pointing at a single hot day or a single flood.

Q4.

India has a tropical monsoon climate, and the Indian Meteorological Department (IMD) divides the year into four main seasons, namely—Winter, Summer, Monsoon, and Post-monsoon.

Answer

What this recap means, expanded. 'Tropical monsoon' is a two-word description doing two jobs: tropical because most of India lies in the torrid zone, between the Tropic of Cancer and the equator, where insolation is high and temperatures stay warm; monsoon because the rain is delivered by a wind that reverses with the seasons.

Season	Months	What the chapter says about it
Winter	December to early April	Coldest months are December and January. Average temperature in the north-west about 10–15°C, rising towards the equator to 20–25°C in mainland India's south-east
Summer or pre-monsoon	April to June (to July in north-western India)	Hottest month is April in western and southern regions, May in the north. Average across most of inland India 32–40°C
Monsoon or rainy (advancing monsoon)	June to September	Dominated by the humid south-west summer monsoon, which sweeps across the country in late May or early June. Rain begins to recede from north India at the beginning of October, and South India typically receives more rainfall during this time
Post-monsoon (retreating monsoon)	October to December	In north-western India, October and November are usually cloudless

Two additions the chapter makes to this four-fold scheme:

The Himalayan states, being more temperate, experience two additional seasons — autumn and spring.
Traditionally India recognises six seasons (ṛtus) of about two months each — Vasanta, Grīṣhma, Varṣhā, Śharad, Hemanta, Śhiśhira — based on the astronomical division of the twelve months into six parts, and reflected in the arrangement of months in the traditional Indian calendar (Table 3.2).

Why the temperature figures rise as you move south: because insolation decreases from the equator towards the poles. The north-west of India is furthest from the equator, so its winter average is 10–15°C; the south-east is nearest, so the same months there average 20–25°C. The same rule that sorts the Earth into torrid, temperate and frigid zones (Fig. 3.6) is at work inside India itself — and Table 3.3 shows it station by station.

Did you know? The interest in measuring the monsoon is very old in India. Kauṭilya's Arthaśhāstra records scientific measurements of rainfall and their use in managing revenue and relief; Kṛiṣhiparāśhara predicted rain from the positions of the Moon and the Sun, and Varāhamihira's Bṛihatsaṁhitā from the lunar mansions (nakṣhatras). Today the same task is carried out by the IMD, the National Monsoon Mission and Mission Mausam.

Q5.

Climate change is the long-term change in weather caused mainly by human activities like burning fuels and cutting trees, which leads to global warming and extreme weather conditions.

Answer

What this recap means, expanded. The chapter builds this as a chain of cause and effect, and it is worth setting out as a chain, because every step of it is also a place to intervene.

Human activities — burning fossil fuels, deforestation, industrial pollution
    ↓
More greenhouse gases in the atmosphere — carbon dioxide, methane, nitrous oxide, water vapour
    ↓
These gases trap heat that would otherwise escape to space
    ↓
Global temperatures rise
    ↓
More frequent floods, droughts, melting of glaciers, rising sea levels, loss of biodiversity

The consequences do not stop at the environment. The chapter is explicit that climate change 'not only threatens ecosystems but also impacts human health, agriculture, and livelihoods', and that it 'has great impact on almost all sections of the population including women and children'.

Why trapping heat is not in itself a bad thing — and where it goes wrong: the very first page of this chapter says the atmosphere 'regulates the Earth's temperature by trapping some of the Sun's energy and prevents it from escaping back into space'. That trapping is what makes the Earth warm enough to live on. The problem is not the greenhouse effect but its increase: adding more of these gases traps more heat than the system was balanced for, and the balance shifts. Notice too that carbon dioxide is only 0.04% of the atmosphere — proof that a very small share of a mixture can have a very large effect.

Connect it to the case study: the Punjab floods of 2025 are the chapter's own illustration of 'extreme weather conditions' — very heavy monsoon rain, intensified by western disturbances, falling on rivers already running high.

Q6.

We can reduce our carbon footprint by saving energy, using renewable sources, planting trees, and living in more eco-friendly ways.

Answer

What this recap means, expanded. A carbon footprint is the total amount of greenhouse gases released into the atmosphere as a result of human activities — energy use, transportation, and the production of goods and services. So reducing it means changing one of those three.

The recap's four actions	What it means in practice	Why it reduces the footprint
Saving energy	Switching off lights and fans when not in use; using water judiciously; walking or cycling instead of taking a car	Most electricity still comes from burning fossil fuels, so energy saved is carbon not released
Using renewable sources	Solar and wind energy instead of coal, oil and gas	They generate power without burning anything, so no carbon dioxide is added
Planting trees	Planting and, just as importantly, protecting existing forests	Growing trees absorb carbon dioxide from the air; deforestation releases what was stored
Living in eco-friendly ways	Reusing and recycling, avoiding single-use plastics, buying less and repairing more	Every manufactured object carries the greenhouse gases released in producing it

Why the chapter asks students to score themselves rather than simply telling them the answer: because a footprint is not a fact about the world, it is a record of choices — and you cannot change a choice you have not noticed. The four sections of the LET'S EXPLORE scorecard (transport, electricity, water, waste and plastics) turn an abstract idea into four things you actually did this week, and the two pledges turn them into two things you will do next week.

Keep the chapter's own last word: 'Every small step counts, and every human being plays a vital role in shaping a healthier and greener future.'

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